/*
 * jdatasrc.cpp
 *
 * Copyright (C) 1994-1996, Thomas G. Lane.
 * This file is part of the Independent JPEG Group's software.
 * For conditions of distribution and use, see the accompanying README file.
 *
 * This file contains decompression data source routines.
 *
 *
 * CIDJPEG: This file has been modified to work solely in terms of our CIDLib
 * binary streaming system, which already abstracts data sources and targets.
 */

/* this is not a core library module, so it doesn't define JPEG_INTERNALS */
#include "CIDLib.hpp"

extern "C"
{
    #include "jinclude.h"
    #include "jpeglib.h"
    #include "jerror.h"
}


/* Expanded data source object for stdio input */

typedef struct
{
    struct jpeg_source_mgr pub;	/* public fields */

    TBinInStream*       pstrmSrc;
    tCIDLib::TCard1*    pc1Buf;
    boolean             start_of_file;	/* have we gotten any data yet? */
}   my_source_mgr;

typedef my_source_mgr * my_src_ptr;

#define INPUT_BUF_SIZE  4096


/*
 * Initialize source --- called by jpeg_read_header
 * before any data is actually read.
 */

METHODDEF(void)
init_source (j_decompress_ptr cinfo)
{
  my_src_ptr src = (my_src_ptr) cinfo->src;

  /* We reset the empty-input-file flag for each image,
   * but we don't clear the input buffer.
   * This is correct behavior for reading a series of images from one source.
   */
  src->start_of_file = TRUE;
}


/*
 * Fill the input buffer --- called whenever buffer is emptied.
 *
 * In typical applications, this should read fresh data into the buffer
 * (ignoring the current state of next_input_byte & bytes_in_buffer),
 * reset the pointer & count to the start of the buffer, and return TRUE
 * indicating that the buffer has been reloaded.  It is not necessary to
 * fill the buffer entirely, only to obtain at least one more byte.
 *
 * There is no such thing as an EOF return.  If the end of the file has been
 * reached, the routine has a choice of ERREXIT() or inserting fake data into
 * the buffer.  In most cases, generating a warning message and inserting a
 * fake EOI marker is the best course of action --- this will allow the
 * decompressor to output however much of the image is there.  However,
 * the resulting error message is misleading if the real problem is an empty
 * input file, so we handle that case specially.
 *
 * In applications that need to be able to suspend compression due to input
 * not being available yet, a FALSE return indicates that no more data can be
 * obtained right now, but more may be forthcoming later.  In this situation,
 * the decompressor will return to its caller (with an indication of the
 * number of scanlines it has read, if any).  The application should resume
 * decompression after it has loaded more data into the input buffer.  Note
 * that there are substantial restrictions on the use of suspension --- see
 * the documentation.
 *
 * When suspending, the decompressor will back up to a convenient restart point
 * (typically the start of the current MCU). next_input_byte & bytes_in_buffer
 * indicate where the restart point will be if the current call returns FALSE.
 * Data beyond this point must be rescanned after resumption, so move it to
 * the front of the buffer rather than discarding it.
 */

METHODDEF(boolean)
fill_input_buffer (j_decompress_ptr cinfo)
{
    my_src_ptr src = (my_src_ptr) cinfo->src;
    size_t nbytes;

    try
    {
        nbytes = src->pstrmSrc->c4ReadRawBuffer
        (
            src->pc1Buf
            , INPUT_BUF_SIZE
            , tCIDLib::EAllData::OkIfNotAll
        );
    }

    catch(...)
    {
        ERREXIT(cinfo, JERR_FILE_READ);
    }

    // Treat zero size as an error
    if (!nbytes)
        ERREXIT(cinfo, JERR_INPUT_EMPTY);

    src->pub.next_input_byte = src->pc1Buf;
    src->pub.bytes_in_buffer = nbytes;
    src->start_of_file = FALSE;

    return TRUE;
}


/*
 * Skip data --- used to skip over a potentially large amount of
 * uninteresting data (such as an APPn marker).
 */
METHODDEF(void)
skip_input_data (j_decompress_ptr cinfo, long num_bytes)
{
    my_src_ptr src = (my_src_ptr) cinfo->src;

    if (num_bytes > 0)
    {
        while (num_bytes > (long) src->pub.bytes_in_buffer)
        {
            num_bytes -= (long) src->pub.bytes_in_buffer;
            fill_input_buffer(cinfo);
        }
        src->pub.next_input_byte += (size_t) num_bytes;
        src->pub.bytes_in_buffer -= (size_t) num_bytes;
    }
}


/*
 * An additional method that can be provided by data source modules is the
 * resync_to_restart method for error recovery in the presence of RST markers.
 * For the moment, this source module just uses the default resync method
 * provided by the JPEG library.  That method assumes that no backtracking
 * is possible.
 */


/*
 * Terminate source --- called by jpeg_finish_decompress
 * after all data has been read.  Often a no-op.
 *
 * NB: *not* called by jpeg_abort or jpeg_destroy; surrounding
 * application must deal with any cleanup that should happen even
 * for error exit.
 */

METHODDEF(void)
term_source (j_decompress_ptr cinfo)
{
  /* no work necessary here */
}


/*
 * Prepare for input via our binary stream.
 */

GLOBAL(void)
jpeg_stdio_src (j_decompress_ptr cinfo, TBinInStream* pstrmSrc)
{
    my_src_ptr src;

    /* The source object and input buffer are made permanent so that a series
     * of JPEG images can be read from the same file by calling jpeg_stdio_src
     * only before the first one.  (If we discarded the buffer at the end of
     * one image, we'd likely lose the start of the next one.)
     * This makes it unsafe to use this manager and a different source
     * manager serially with the same JPEG object.  Caveat programmer.
     */

    /* first time for this JPEG object? */
    if (cinfo->src == NULL)
    {	
        cinfo->src = (struct jpeg_source_mgr *)
          (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
        			  SIZEOF(my_source_mgr));
        src = (my_src_ptr) cinfo->src;
        src->pc1Buf = (tCIDLib::TCard1*)
          (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
        			  INPUT_BUF_SIZE * SIZEOF(JOCTET));
    }

    src = (my_src_ptr) cinfo->src;
    src->pub.init_source = init_source;
    src->pub.fill_input_buffer = fill_input_buffer;
    src->pub.skip_input_data = skip_input_data;
    src->pub.resync_to_restart = jpeg_resync_to_restart; /* use default method */
    src->pub.term_source = term_source;

    src->pstrmSrc = pstrmSrc;
    src->pub.bytes_in_buffer = 0; /* forces fill_input_buffer on first read */
    src->pub.next_input_byte = NULL; /* until buffer loaded */
}

